Negative electrode material for nonaqueous electrolyte secondary battery, and nonaqueous electrolyte secondary battery using the same

ABSTRACT

A negative electrode material for a nonaqueous electrolyte secondary battery, where the negative electrode contains a carbon material A and a carbon material B. Carbon material A is a multilayer-structure carbon material containing a graphitic particle having an amorphous carbon surface covering, where the interplaner spacing of 002 planes, by wide-angle XRD, is 3.37 Å or less, Lc is 900 Å or more, the tap density is 0.8 g/cm 3  or more, and the Raman R value is from 0.25 to 0.6. Carbon material B is a graphitic particle where the interplanar spacing of 002 planes, by wide-angle XRD, is 3.37 Å or less, Lc is 900 Å or more, the tap density is 0.8 g/cm 3  or more, the Raman R value is from 0.2 to 0.5, and the average degree of circularity, determined by a flow-type particle analyzer, is 0.9 or more.

TECHNICAL FIELD

The present invention relates to a carbon material for negativeelectrode of a nonaqueous electrolyte secondary battery. The presentinvention also relates to a negative electrode for nonaqueouselectrolyte secondary battery using the negative electrode carbonmaterial, and a nonaqueous electrolyte secondary battery having thenegative electrode.

BACKGROUND ART

A nonaqueous lithium secondary battery comprising positive and negativeelectrodes capable of storing/releasing lithium ion and a nonaqueouselectrolytic solution having dissolved therein a lithium salt such asLiPF₆ and LiBF₄ has been developed and is used in practice.

Various materials have been proposed as the negative electrode materialof this battery, but in view of high capacity and excellent flatness ofdischarge potential, a graphitic carbon material such as naturalgraphite, artificial graphite obtained by graphitizing coke or the like,graphitized mesophase pitch, and graphitized carbon fiber is used.

Also, an amorphous carbon material is used because this is relativelystable to some electrolytic solutions. In addition, a carbon materialimparted with properties of both graphite and amorphous carbon bycoating or attaching amorphous carbon on the surface of a graphiticcarbon particle is also used.

In Patent Document 1, a spheroidized graphitic carbon material enhancedin the rapid charge-discharge characteristics by applying a mechanicalenergy treatment to a graphitic carbon particle that is originally in aflake, scale or plate form, to give a damage to the graphitic particlesurface and at the same time, spheroidize the particle is used, and itis further proposed to use a spheroidized carbon material having amultilayer structure, which has the properties of graphite and amorphouscarbon by virtue of coating or attaching amorphous carbon on the surfaceof the spheroidized graphitic carbon particle and simultaneously hasrapid charging-discharging property.

However, in recent years, the application of a nonaqueous lithiumsecondary battery is expanding, and a nonaqueous lithium secondarybattery having higher rapid charging-discharging property than everbefore and at the same time, having high cycle characteristics isdemanded in use for electric power tools, electric cars and the like, inaddition to conventional use for notebook-size personal computers,mobile communication equipment, portable cameras, potable game machinesand the like.

With respect to improvement of the cycle characteristics, for example,Patent Document 2 has proposed a nonaqueous lithium secondary batteryusing, as negative electrode materials, a carbonaceous material particlehaving a multilayer structure, where the R value obtained from the Ramanspectrum is 0.2 or more, and an amorphous carbonaceous particle havinglow crystallinity, where the X-ray interplanar spacing d002 is from 3.36to 3.60 Å. However, this battery has a problem that the irreversiblecapacity attributable to the amorphous carbon particle is increased, andmore improvements are needed on the cycle characteristics and rapidcharge-discharge characteristics required of the recent lithiumsecondary battery.

Also, Patent Document 3 has proposed a negative electrode materialcomposed of a mixture of a coated graphite particle whose surface iscovered with amorphous carbon, and a non-coated graphite particle whosesurface is not covered with amorphous carbon.

In the description of Patent Document 3, it is stated that thenon-coated graphite particle indicates a graphite particle where theratio [I1360/I1580] of the peak intensity (I1360) near 1,360 cm⁻¹ to thepeak intensity (I1580) near 1,580 cm⁻¹ in argon laser Raman spectrometryat a wavelength of 5,145 Å is 0.10 or less. It is also stated that thecoated graphite particle indicates a graphite particle where the ratio[I1360/I1580] of the peak intensity (11360) near 1,360 cm⁻¹ to the peakintensity (I1580) near 1,580 cm⁻¹ in argon laser Raman spectrometry at awavelength of 5,145 Å is from 0.13 to 0.23.

RELATED ART Patent Document

-   Patent Document 1: Japanese Patent No. 3534391-   Patent Document 2: Japanese Patent No. 3291756-   Patent Document 3: JP-A-2005-294011 (the term “JP-A” as used herein    means an “unexamined published Japanese patent application”)

SUMMARY OF THE INVENTION Problems that the Invention is to Solve

However, the targeted high capacity, rapid charging-discharging propertyand cycle characteristics sought by the present inventors have not beenachieved even by the methods described above.

Accordingly, an object of the present invention is to propose a negativeelectrode material for nonaqueous electrolyte secondary battery, havinghigh capacity and satisfying both rapid charge-discharge characteristicsand high cycle characteristics, which is suited also for the recentapplication to electric power tools or electric cars.

Means for Solving the Problems

As a result of intensive studies to attain the above-described object,the present inventors have found that when a negative electrode materialcontaining two kinds of carbon materials, that is, carbon material A andcarbon material B, differing in the role is used, an electrode fornonaqueous electrolyte secondary battery, satisfying both rapidcharge-discharge characteristics and cycle characteristics, can beobtained. The present invention has been accomplished based on thisfinding.

A material excellent particularly in the rapid charging-dischargingproperty is selected for the carbon material A, and a material excellentparticularly in the conductivity is selected for the carbon material B.However, both the carbon material A and the carbon material B must be acarbon material having both high capacity and rapid charge-dischargecharacteristics.

The carbon material A having both high capacity and rapidcharge-discharge characteristics and being excellent particularly in therapid charge-discharge characteristics is a multilayer-structure carbonmaterial containing a graphitic particle and an amorphous carboncovering the surface thereof, which is a carbon material where theinterplanar spacing (d002) of 002 planes of the multilayer-structurecarbon material as measured by the wide-angle X-ray diffraction methodis 3.37 Å or less, Lc is 900 Å or more, the tap density is 0.8 g/cm³ ormore, and the Raman R value that is a ratio of the peak intensity near1,360 cm⁻¹ to the peak intensity near 1,580 cm⁻¹ in the argon ion laserRaman spectrum is from 0.25 to 0.6.

The carbon material B having both high capacity and rapid dischargecharacteristics and being excellent particularly in the electronconductivity is a graphitic particle where the interplanar spacing(d002) of 002 planes by the wide-angle X-ray diffraction method is 3.37Å or less, Lc is 900 Å or more, the tap density is 0.8 g/cm³ or more,the Raman R value that is a ratio of the peak intensity near 1,360 cm⁻¹to the peak intensity near 1,580 cm⁻¹ in the argon ion laser Ramanspectrum is from 0.2 to 0.5, and the average degree of circularity asdetermined by a flow-type particle analyzer is 0.9 or more.

That is, the present invention is as follows.

1. A negative electrode material for nonaqueous electrolyte secondarybattery, comprising the following carbon material A and carbon materialB:

(Carbon Material A)

a multilayer-structure carbon material containing a graphitic particleand an amorphous carbon covering the surface of the graphitic particle,which is a carbon material where the interplanar spacing (d002) of 002planes by the wide-angle X-ray diffraction method is 3.37 Å or less, Lcis 900 Å or more, the tap density is 0.8 g/cm³ or more, and the Raman Rvalue that is a ratio of the peak intensity near 1,360 cm⁻¹ to the peakintensity near 1,580 cm⁻¹ in the argon ion laser Raman spectrum, is from0.25 to 0.6,

(Carbon Material B)

a graphitic particle where the interplanar spacing (d002) of 002 planesby the wide-angle X-ray diffraction method is 3.37 Å or less, Lc is 900Å or more, the tap density is 0.8 g/cm³ or more, the Raman R value thatis a ratio of the peak intensity near 1,360 cm⁻¹ to the peak intensitynear 1,580 cm⁻¹ in the argon ion laser Raman spectrum, is from 0.2 to0.5, and the average degree of circularity as determined by a flow-typeparticle analyzer is 0.9 or more.

2. The negative electrode material for nonaqueous electrolyte secondarybattery as described in 1 above, wherein the ratio in the averageparticle diameter between the carbon material A and the carbon materialB (average particle diameter of carbon material A/average particlediameter of carbon material B) is from 0.7 to 1.3.

3. The negative electrode material for nonaqueous electrolyte secondarybattery as described in 1 or 2 above, wherein the ratio of the carbonmaterial Bis from 30 to 70 wt % based on the total amount of the carbonmaterial A and the carbon material B.

4. The negative electrode material for nonaqueous electrolyte secondarybattery as described in any one of 1 to 3 above, wherein in thegraphitic particle used for the carbon material A, the interplanarspacing (d002) of 002 planes by the wide-angle X-ray diffraction methodis 3.37 Å or less, Lc is 900 Å or more, the tap density is 0.8 g/cm³ ormore, and the Raman R value that is a ratio of the peak intensity near1,360 cm⁻¹ to the peak intensity near 1,580 cm⁻¹ in the argon ion laserRaman spectrum is from 0.2 to 0.5.

5. The negative electrode material for nonaqueous electrolyte secondarybattery as described in any one of 1 to 4 above, wherein the tap densityis 0.8 g/cm³ or more.

6. The negative electrode material for nonaqueous electrolyte secondarybattery as described in any one of 1 to 5 above, wherein the truedensity of the carbon material B is 2.21 g/cm³ or more.

7. The negative electrode material for nonaqueous electrolyte secondarybattery as described in any one of 1 to 6 above, wherein the specificsurface area of the carbon material A is from 0.5 to 8 m²/g.

8. The negative electrode material for nonaqueous electrolyte secondarybattery as described in any one of 1 to 7 above, wherein the averagedegree of circularity of the graphitic particle used for the carbonmaterial A as determined by a flow-type particle analyzer is 0.88 ormore.

9. The negative electrode material for nonaqueous electrolyte secondarybattery as described in any one of 1 to 8 above, wherein the porevolumes in the range of 10 to 100,000 nm of the carbon material A andthe carbon material B as measured by the mercury intrusion method, are0.4 ml/g or more.

10. The negative electrode material for nonaqueous electrolyte secondarybattery as described in any one of 1 to 9 above, wherein the averageparticle diameter of the carbon material A is from 2 to 30 μM.

11. A negative electrode for nonaqueous electrolyte secondary battery,comprising: a current collector; and a negative electrode layer providedthereon, wherein the negative electrode layer contains the negativeelectrode material for nonaqueous electrolyte secondary batterydescribed in any one of 1 to 10 and a binder resin.

12. A nonaqueous electrolyte secondary battery comprising the negativeelectrode described in 11 above, a positive electrode capable ofstoring/releasing lithium ion, and a nonaqueous electrolytic solution.

Advantage of the Invention

A nonaqueous electrolyte secondary battery using, as an electrode, thenegative electrode material for nonaqueous electrolyte secondary batteryof the present invention exhibits an excellent property satisfying bothrapid charge-discharge characteristics and high cycle characteristics.

MODE FOR CARRYING OUT THE INVENTION

The negative electrode material for nonaqueous electrolyte secondarybattery of the present invention (hereinafter, sometimes referred to asthe negative electrode material of the present invention) is a negativeelectrode material for nonaqueous electrolyte secondary battery,containing at least the following carbon material A and carbon materialB:

(Carbon Material A)

a multilayer-structure carbon material containing a graphitic particleand an amorphous carbon covering the surface thereof, which is a carbonmaterial where the interplanar spacing (d002) of 002 planes by thewide-angle X-ray diffraction method is 3.37 Å or less, Lc is 900 Å ormore, the tap density is 0.8 g/cm³ or more, and the Raman R value thatis a ratio of the peak intensity near 1,360 cm⁻¹ to the peak intensitynear 1,580 cm⁻¹ in the argon ion laser Raman spectrum is from 0.25 to0.6,

(Carbon Material B)

a graphitic particle where the interplanar spacing (d002) of 002 planesby the wide-angle X-ray diffraction method is 3.37 Å or less, Lc is 900Å or more, the tap density is 0.8 g/cm³ or more, the Raman R value thatis a ratio of the peak intensity near 1,360 cm⁻¹ to the peak intensitynear 1,580 cm⁻¹ in the argon ion laser Raman spectrum is from 0.2 to0.5, and the average degree of circularity as determined by a flow-typeparticle analyzer is 0.9 or more.

[Carbon Material A]

(a) Interplanar Spacing (d002) of 002 Planes

In the carbon material A, the interplanar spacing (d002) of 002 planesby the wide-angle X-ray diffraction method is 3.37 Å or less, and Lc is900 Å or more. It is preferred that the interplanar spacing (d002) of002 planes is 3.36 Å or less and Lc is 950 Å or more. The interplanarspacing (d002) of 002 planes by the wide-angle X-ray diffraction methodis measured by the method described later in Examples. When theinterplanar spacing (d002) of 002 planes is 3.37 Å or less and Lc is 900Å or more, this indicates that the carbon material has highcrystallinity in most portions excluding the surface of a particlethereof and is a carbon material working out to a high-capacity negativeelectrode material free from capacity reduction due to such a largeirreversible capacity as seen in an amorphous carbon material.

(b) Tap Density

The tap density of the carbon material A is 0.8 g/cm³ or more,preferably 0.85 cm³ or more. The tap density is measured by the methoddescribed later in Examples. The tap density being 0.8 g/cm³ or moreindicates that the carbon material provides a spherical appearance.

If the tap density is less than 0.8 g/cm³, this indicates that thespherical graphitic particle as a raw material of the carbon material Ais not formed as an adequately spherical particle, and in this case, acontinuous void is not sufficiently ensured in the electrode and themobility of Li ion in the electrolytic solution held in the void isimpaired, giving rise to reduction in the rapid charge-dischargecharacteristics.

(c) Raman R Value

In the carbon material A, the Raman R value that is a ratio of the peakintensity near 1,360 cm⁻¹ to the peak intensity near 1,580 cm⁻¹ in theargon ion laser Raman spectrum is from 0.25 to 0.6, preferably from 0.25to 0.5, more preferably from 0.25 to 0.4. The Raman R value is measuredby the method described later in Examples.

Studies by the present inventors have revealed that the targeted rapidcharge-discharge characteristics are not achieved when using a carbonmaterial in which the Raman R value of the multilayer-structure carbonmaterial for electrode is 0.25 or less.

The Raman R value of the multilayer-structure carbon material isgoverned by the Raman R value of the graphitic particle and the Raman Rvalue of the covering amorphous carbon coated on the surface of thegraphitic carbon. If the Raman R value of the multilayer-structurecarbon material is low, this indicates that the Raman R value of thegraphitic particle is low and the graphitic particle is not aspheroidized particle having received on the particle surface thereof asufficient damage by a mechanical energy treatment, and in this case,the amount of sites for receiving or releasing Li ion, such as finecrack, chipping and structural defect on the graphitic particle surfacedue to damage, is small, giving rise to bad rapid charging-dischargingproperty for Li ion.

Also, if the Raman R value of the carbon material A exceeds 0.6, thisindicates that the amount of the amorphous carbon covering the graphiticparticle is large, and in this case, the effect on the magnitude ofirreversible capacity by the amorphous carbon amount is increased and asmall battery capacity results.

When the Raman R is 0.25 or more, this indicates that the carbonmaterial is a multilayer-structure carbon material containing agraphitic particle and an amorphous carbon covering the surface thereofand at the same time, the spherical graphitic particle surface has afine crack, chipping, a structural defect or the like created due todamage by a mechanical energy treatment.

That is, the carbon material A is a material obtained by a process wherea flat graphitic particle is spheroidized while involving folding,winding or chamfering and at the same time, the surface of the graphiticparticle having formed on the particle surface thereof a fine crack,chipping, a structural defect or the like is covered with an amorphouscarbon.

Also, the carbon material A is a spheroidized particle enjoying high Liion acceptability of the amorphous carbon and thanks to a fine crack,chipping or a structural defect on the surface of the graphitic particleworking as a core, allowing Li ion to easily enter or leave the insideof the graphite crystal, and therefore, this is a carbon materialcapable of ensuring communicating voids in the electrode and by asynergistic effect with good mobility of Li ion, enhancing the rapidcharging-discharging property.

At the same time, the carbon material A is a carbon material having bothhigh capacity by virtue of the particle body being graphitic except forthe particle surface, and low irreversible capacity because theamorphous carbon covering the graphitic particle surface produces aneffect of suppressing an excessive reaction with an electrolyticsolution.

(d) 3R/2H

The wide-angle X-ray diffraction method is used to determine a valueindicative of crystallinity of the entire particle, and the argon ionlaser Raman spectrum is utilized to determine a value indicative of thesurface property of a particle. As for the wide-angle X-ray diffractionmethod, the measurement is performed by the method described later inExamples. In the carbon material A, the ratio 3R/2H between theintensity 3R(101) of 101 plane based on the rhombohedral crystalstructure and the intensity 2H(101) of 101 plane based on the hexagonalcrystal structure, as determined by the wide-angle X-ray diffractionmethod, is preferably 0.1 or more, more preferably 0.2 or more.

The rhombohedral crystal structure is a crystal morphology where a stackof graphite network plane structures is repeated for every three layers.Also, the hexagonal crystal structure is a crystal morphology where astack of graphite network plane structures is repeated for every twolayers. In the case of a graphitic particle showing a crystal morphologywhere the ratio of the rhombohedral crystal structure 3R is large, Liion acceptability is high compared with a graphite particle where theratio of the rhombohedral crystal structure 3R is small.

(e) Specific Surface Area by BET Method

The specific surface area of the carbon material A by the BET method ispreferably from 0.5 to 8 m²/g, more preferably from 1 to 6 m²/g, stillmore preferably from 1.5 to 5 m²/g. The specific surface area by the BETmethod is measured by the method described later in Examples.

By setting the specific surface area of the carbon material A to 0.5m²/g or more, the Li ion acceptability is enhanced, and by setting it to8 m²/g or less, the battery capacity can be prevented from reduction dueto increase in the irreversible capacity.

(f) Pore Volume

The pore volume of the carbon material A by the mercury intrusion methodin the range of 10 to 100,000 nm is preferably 0.4 ml/g or more, morepreferably 0.5 ml/g or more. The pore volume is measured by the methoddescribed later in Examples. By setting the pore volume to 0.4 ml/g ormore, the area for entering/leaving of Li ion is increased.

(g) Average Particle Diameter

The average particle diameter of the carbon material A is preferablyfrom 2 to 30 μm, more preferably from 4 to 20 μm, still more preferablyfrom 6 to 15 μm. The average particle diameter is measured by the methoddescribed later in Examples. By setting the average particle diameter to2 μm more, the irreversible capacity can be prevented from increasingdue to a large specific surface area, and by setting it to 30 μm orless, the rapid charging-discharging property can be prevented fromdeterioration due to decrease in the contact area of the electrolyticsolution with the carbon material A particle.

(h) Interplanar Spacing (d002) of 002 Planes of Graphitic Particle

In the graphitic particle before covering with an amorphous carbon, usedin the carbon material A, the interplanar spacing (d002) of 002 planesby the X-ray diffraction method is preferably 3.37 Å or less, and Lc ispreferably 900 Å or more. When the interplanar spacing (d002) of 002planes by the wide-angle X-ray diffraction method is 3.37 Å or less andLc is 900 Å or more, this indicates that the carbon material A has highcrystallinity in most portions excluding the surface of a particlethereof and is a carbon material working out to a high-capacityelectrode free from capacity reduction due to such a large irreversiblecapacity as seen in an amorphous carbon material.

(i) Tap Density of Graphitic Particle

The tap density of the graphitic particle before covering its surfacewith an amorphous carbon, used in the carbon material A, is preferably0.8 g/cm³ or more. When the tap density of the graphitic particle beforecovering is 0.8 g/cm³ or more, a carbon material satisfying both highcapacity and rapid discharge characteristics can be obtained.

(j) Raman K Value of Graphitic Particle

In the graphitic particle before covering with an amorphous carbon, usedin the carbon material A, the Raman R value that is a ratio of the peakintensity near 1,360 cm⁻¹ to the peak intensity near 1,580 cm⁻¹ in theargon ion laser Raman spectrum is preferably from 0.2 to 0.5, morepreferably from 0.2 to 0.4.

When the Raman R value is 0.2 or more, this indicates that a fine crack,chipping, a structural defect or the like is created in the graphiticparticle surface due to a damage given by applying a mechanical energytreatment in the process of spheroidizing the graphitic particle. Also,when the Raman R value is 0.5 or less, this indicates that themechanical energy treatment is not so excessive as destroying thecrystal structure itself of the graphitic particle and the batterycapacity is kept from reduction due to increase in the irreversiblecapacity caused by destruction of the crystal structure of the graphiticparticle.

(k) Average Degree of Circularity of Graphitic Particle

As to the average degree of circularity, in a flow-type particleanalyzer capable of individually photographing thousands of particlesdispersed in a liquid by using a CCD camera and calculating the averageprofile parameter, the measurement is performed for particles in therange from 10 to 40 μm by the method described later in Examples. Theaverage degree of circularity is a ratio using the circumferentiallength of a circle corresponding to the particle area as the numeratorand using the circumferential length of a projected particle imagephotographed as the denominator, As the particle image is closer to atrue circle, the value approximates 1, and as the particle image islonger/thinner or more irregular, the value becomes smaller.

The average degree of circularity of the graphitic particle beforecovering its surface with an amorphous carbon, used in the carbonmaterial A, is preferably 0.88 or more. Also, the graphitic particle ispreferably a spheroidized graphitic particle. By setting the averagedegree of circularity of the graphic particle before covering to 0.88 ormore, a carbon material satisfying both high capacity and rapiddischarge characteristics can be obtained.

(l) Interplanar Spacing (d002) of 002 Planes of Amorphous Carbon

In the amorphous carbon covering the surface of the graphitic particle,used in the carbon material A, the interplanar spacing (d002) of 002planes by the wide-angle X-ray diffraction method is preferably 3.40 Åor less, and Lc is preferably 500 Å or more. When the interplanarspacing (d002) of 002 planes is 3.40 Å or less and Lc is 500 Å or more,the Li ion acceptability can be enhanced.

(m) Production Method of Carbon Material A

The carbon material A may be produced without problem by any productionmethod as long as it has the above-described properties, but, forexample, a multilayer-structure carbon material for electrode describedin Japanese Patent No. 3,534,391 may be used. Specifically, for example,a mechanical energy treatment is applied to a naturally-producedflake-like, scale-like, plate-like or lump-like graphite or anartificial graphite produced by heating petroleum coke, coal pitch coke,coal needle coke, mesophase pitch or the like at 2,500° C. or more,whereby the graphitic particle before covering can be produced.

In the mechanical energy treatment, for example, an apparatus with arotor having a large number of blades provided inside a casing is used,and the rotor is rotated at a high speed to repeatedly apply amechanical action such as impact compression, friction and shear forceto the natural graphite or artificial graphite introduced into theinside of the rotor, whereby the carbon material can be produced.

The carbon material A can be obtained by mixing the above-describedgraphitic particle with a petroleum-based or coal-based tar or pitch anda resin such as polyvinyl alcohol, polyacryl nitrile, phenolic resin andcellulose by using, if desired, a solvent or the like, and firing themixture in a non-oxidizing atmosphere at 500 to 2,500° C., preferablyfrom 700 to 2,000° C., more preferably from 800 to 1,500° C. If desired,pulverization and classification are sometimes performed after thefiring.

The coverage that is the amount of the amorphous carbon covering thegraphite particle is preferably from 0.1 to 20%, more preferably from0.2 to 15%, still more preferably from 0.4 to 10%. The coverage can bedetermined by the method described later in Examples.

By setting the coverage to 0.1% or more, high Li ion acceptability ofthe amorphous carbon can be fully utilized and good rapid chargingproperty is obtained. Also, by setting the coverage to 20% or less, thecapacity reduction due to increase in the effect of the amorphous carbonamount on the magnitude of irreversible capacity can be prevented.

[Carbon Material B]

(a) Interplanar Spacing (d002) of 002 Planes

In the carbon material B, the interplanar spacing (d002) of 002 planesby the wide-angle X-ray diffraction method is 3.37 Å or less, and Lc is900 Å or more. When the interplanar spacing (d002) of 002 planes by thewide-angle X-ray diffraction method is 3.37 Å or less and Lc is 900 Å ormore, this indicates that the carbon material has high crystallinity inmost portions excluding the surface of a particle thereof and is acarbon material working out to a high-capacity electrode free fromcapacity reduction due to such a large irreversible capacity as seen inan amorphous carbon material,

(b) Tap Density

The tap density of the carbon material B is preferably 0.8 g/cm³ ormore. The tap density of the carbon material B being 0.8 g/cm³ or moreindicates that the carbon material A provides a spherical appearance.

If the tap density is less than 0.8 g/cm³, this indicates that thespherical graphitic particle is not formed as an adequately sphericalparticle, and in this case, sufficient communicating voids are notensured in the electrode and the mobility of Li ion in the electrolyticsolution held in the void is impaired, giving rise to reduction in therapid charge-discharge characteristics.

(c) Raman R Value

In the carbon material B, the Raman R value that is a ratio of the peakintensity near 1,360 cm⁻¹ to the peak intensity near 1,580 cm⁻¹ in theargon ion laser Raman spectrum is from 0.2 to 0.5, preferably from 0.2to 0.4.

When the Raman R value is 0.2 or more, this indicates that a fine crack,chipping, a structural defect or the like is created in the graphiticparticle surface due to a damage given by applying a mechanical energytreatment in the process of spheroidizing the graphitic carbon particle.Also, when the Raman R value is 0.5 or less, this indicates that themechanical energy treatment is not so excessive as destroying thecrystal structure itself of the graphitic particle and the batterycapacity is kept from reduction due to increase in the irreversiblecapacity caused by destruction of the crystal structure of the graphiticparticle.

That is, it is indicated that the carbon material B is a graphiticparticle obtained by spheroidizing a flat graphite particle whileinvolving folding, winding or chamfering, and at the same time, creatinga fine crack, chipping, a structural defect or the like on the particlesurface. Also, it is indicated that the carbon material B is a carbonmaterial enhanced in the rapid charging-discharging property by asynergistic effect between easy entering of Li ion into the graphitebulk crystal thanks to a fine crack, chipping or a structural defect onthe particle surface and good Li ion mobility by ensuring voids in theelectrode because of a spheroidized particle.

(d) Average Degree of Circularity

The average degree of circularity measured as above of the carbonmaterial B is 0.9 or more. If the average degree of circularity is lessthan 0.9, the effects of the present invention may not be obtained. Thecarbon material B is preferably a spheroidized graphitic particle.

(e) 3R/2H

In the carbon material B, the ratio 3R/2H between the intensity 3R(101)of 101 plane based on orientation of a rhombohedral graphite layer andthe intensity 2H(101) of 101 plane based on orientation of a hexagonalgraphite layer, as determined by the wide-angle X-ray diffractionmethod, is preferably 0.1 or more, more preferably 0.15 or more. In thecase of a graphitic particle showing a crystal morphology where theratio of the rhombohedral crystal structure 3R is large, Li ionacceptability is high compared with a graphite particle where the ratioof the rhombohedral crystal structure 3R is small.

(f) True Density

The true density of the carbon material B is preferably 2.21 g/cm³ ormore, more preferably 2.23 g/cm³ or more, still more preferably 2.25g/cm³ or more. The true density being 2.21 g/cm³ or more indicates thatthe main body of the graphite particle has high crystallinity and inturn, the carbon material is a high-capacity carbon material with smallirreversible capacity.

(g) Specific Surface Area by BET Method

The specific surface area of the carbon material B by the BET method ispreferably from 12 m²/g or less, more preferably 10 m²/g or less, and ispreferably 1 m²/g or more, more preferably 1.5 m²/g or more.

By setting the specific surface area of the carbon material B to 12 m²/gor less, the capacity can be prevented from reduction due to increase inthe irreversible capacity. Also, by setting the specific surface area to1 m²/g or more, the area for receiving or releasing lithium is increasedand an electrode excellent in rapid charging or rapid dischargingproperty can be obtained.

(h) Pore Volume

The pore volume of the carbon material B by the mercury intrusion methodin the range of 10 to 100,000 nm is preferably 0.4 ml/g or more, morepreferably 0.5 ml/g or more. By setting the pore volume to 0.4 ml/g ormore, the area for entering/leaving of Li ion is increased.

(i) Average Particle Diameter

The average particle diameter of the carbon material B is preferablyfrom 2 to 30 μm, more preferably from 4 to 20 μm, still more preferablyfrom 6 to 15 p.m. By setting the average particle diameter to 2 μm ormore, the irreversible capacity can be prevented from increasing due toa large specific surface area, and by setting the average particlediameter to 30 μm or less, the rapid charging-discharging property canbe prevented from reduction due to decrease in the contact area of theelectrolytic solution with the carbon material B particle.

(j) Production Method of Carbon Material B

The carbon material B may be produced without problem by any productionmethod as long as it has the above-described properties, but, forexample, a carbon material for electrode described in Japanese PatentNo. 3,534,391 may be used. Specifically, for example, a mechanicalenergy treatment is applied to a naturally-produced flake-like,scale-like, plate-like or lump-like graphite or an artificial graphiteproduced by heating petroleum coke, coal pitch coke, coal needle coke,mesophase pitch or the like at 2,500° C. or more, whereby the carbonmaterial can be produced.

In the mechanical energy treatment, for example, an apparatus with arotor having a large number of blades provided inside a casing is used,and the rotor is rotated at a high speed to apply a mechanical actionsuch as impact compression, friction and shear force to the naturalgraphite or artificial graphite introduced into the inside of the rotor,whereby the carbon material can be produced.

Unlike the carbon material A, the carbon material B is not amultilayer-structure carbon material. Because, in the carbon material Awhich is a carbon material enhanced particularly in the rapid chargingproperty by making use of high Li ion acceptability of the amorphouscarbon covering the graphitic particle surface, the electronconductivity is disadvantageously reduced due to surface covering withthe amorphous carbon, as compared with the graphitic particle beforecovering.

On the other hand, the carbon material B is a graphitic carbon whosesurface is not covered with an amorphous carbon, and therefore, this isa material having higher electron conductivity than the carbon materialA, though the rapid charging property is inferior to the carbon materialA whose surface is covered with an amorphous carbon. By mixing thesecarbon material A and carbon material B, an electrode material havingboth rapid charging-discharging property and high electron conductivityand further showing high cycle characteristics due to a combined effectsuch as high electrolytic solution retentivity in an interparticle spaceis obtained.

[Negative Electrode Material for Nonaqueous Electrolyte SecondaryBattery] (a) Mixing Ratio of Carbon Material A and Carbon Material B

The negative electrode material of the present invention is a mixedcarbon material containing the above-described carbon material A andcarbon material B. In the negative electrode material of the presentinvention, the ratio of the carbon material B is preferably from 10 to90 wt %, more preferably from 20 to 80 wt %, still more preferably from30 to 70 wt %, based on the total amount of the carbon material A andthe carbon material B.

By setting the ratio of the carbon material B to 90 wt % or less basedon the total amount of the carbon material A and the carbon material B,rapid charging property attributable to the covering amorphous carbon,which is a particularly excellent property of the carbon material A, canbe prevented from being impaired and good rapid charge characteristicscan be obtained. Also, by setting the ratio of the carbon material B to10 wt % or more, an electrode fully utilizing the electron conductivitythat is a particularly excellent property of the carbon material B canbe fabricated and sufficient cycle characteristics are obtained.

(b) Ratio in Average Particle Diameter Between Carbon Material A andCarbon Material B

In the negative electrode material of the present invention, the ratioin the average particle diameter between the carbon material A and thecarbon material B (average particle diameter of carbon materialA/average particle diameter of carbon material B) is preferably from 0.7to 1.3, more preferably from 0.8 to 1.2.

If the difference in the average particle diameter between the carbonmaterial A and the carbon material B is large, the particle sizedistribution of the mixed carbon material becomes wide and when anelectrode is formed using the mixed carbon material, the space betweenparticles is filled with particles having a small particle diameter, andthe amount of the electrolytic solution held is decreased, making itdifficult for Li ion to move.

On the other hand, when the difference in the average particle diameterbetween the carbon materials mixed is small, that is, when the ratio inthe average particle diameter between the carbon material A and thecarbon material B is from 0.7 to 1.3, the particle size distribution ofthe mixed carbon material becomes narrow and the amount of particles assmall as filling the space between particles is reduced, so that when anelectrode is formed using the carbon material, an adequate interparticlespacing for holding an electrolytic solution can be ensured.

(c) Tap Density

The tap density of the negative electrode material of the presentinvention is preferably 0.8 g/cm³ or more, more preferably 0.85 g/cm³ ormore.

When the tap density of the mixed carbon material B is 0.8 g/cm³ ormore, the mixed carbon material can be an adequately spherical particleto assure communicating voids in the electrode and allow for smoothmovement of Li ion through the electrolytic solution held in the voidand can be a material having excellent rapid charging-dischargingproperty.

[Negative Electrode]

In producing a negative electrode by using the negative electrodematerial of the present invention, the negative electrode materialblended with a binder resin may be made into a slurry with an aqueous ororganic medium and after adding a thickening agent, if desired, theslurry may be coated on a current collector and dried.

As the binder resin, a resin that is stable to a nonaqueous electrolyticsolution and water-insoluble is preferably used. Examples of the resinwhich can be used include a rubbery polymer such as styrene, butadienerubber, isoprene rubber, and ethylene-propylene rubber; a syntheticresin such as polyethylene, polypropylene, polyethylene terephthalate,and aromatic polyamide; a thermoplastic elastomer such asstyrene-butadiene-styrene block copolymer or hydrogenated productthereof, styrene-ethylene-butadiene styrene copolymer, andstyrene-isoprene styrene block copolymer or hydrogenated productthereof; a soft resinous polymer such as syndiotactic-1,2-polybutadiene,ethylene-vinyl acetate copolymer, and copolymer of ethylene and α-olefinhaving a carbon number of 3 to 12; and a fluorinated polymer such aspolytetrafluoroethylene-ethylene copolymer, polyvinylidene fluoride,polypentafluoropropylene, and polyhexafluoropropylene. Examples of theorganic medium include N-methylpyrrolidone and dimethylformamide.

The binder resin is preferably used in an amount of usually 0.1 parts byweight or more, preferably 0.2 parts by weight, per 100 parts by weightof the negative electrode material. When the ratio of the binder resinis 0.1 parts by weight or more per 100 parts by weight of the negativeelectrode material, the binding force between negative electrodematerials or between the negative electrode material and the currentcollector becomes sufficiently high, and decrease in the batterycapacity and deterioration of the cycle characteristics can be preventedfrom occurring due to separation of the negative electrode material fromthe negative electrode.

Also, the binder resin is preferably used in an amount of usually 10parts by weight or less, preferably 7 parts by weight or less, per 100parts by weight of the negative electrode material. When the ratio ofthe binder resin is 10 parts by weight or less per 100 parts by weightof the negative electrode material, decrease in the capacity of thenegative electrode can be prevented and a problem, for example, thatlithium ion is blocked from entering/leaving the negative electrodematerial can be avoided.

As the thickening agent added to the slurry, for example, water-solublecelluloses such as carboxymethyl cellulose, methyl cellulose,hydroxyethyl cellulose and hydroxypropyl cellulose, polyvinyl alcoholand polyethylene glycol may be used. Among these, carboxymethylcellulose is preferred. The thickening agent is preferably used in anamount of usually from 0.1 to 10 parts by weight, preferably from 0.2 to7 parts by weight, per 100 parts by weight of the negative electrodematerial.

As the negative electrode current collector, for example, copper, copperalloy, stainless steel, nickel, titanium and carbon, which areconventionally known to be usable in this application, may be used. Theshape of the current collector is usually a sheet shape, and it is alsopreferred to use a sheet with the surface being made uneven, a net, apunched metal or the like.

After the slurry containing the negative electrode material and a binderresin is coated and dried on a current collector, a pressure ispreferably applied to increase the density of the electrode formed onthe current collector and make large the battery capacity per unitvolume of the negative electrode layer. The density of the electrode ispreferably from 1.2 to 1.8 g/cm³, more preferably from 1.3 to 1.6 g/cm³.

By setting the electrode density to 1.2 g/cm³ or more, the capacity ofthe battery can be prevented from decreasing due to increase in thethickness of the electrode. Also, by setting the electrode density to1.8 g/cm³ or less, the amount of an electrolytic solution held in aspace can be prevented from decreasing due to reduction in theinterparticle spacing inside the electrode to impair the mobility of Liion and deteriorate the rapid charging-discharging property.

[Nonaqueous Electrolyte Secondary Battery]

The nonaqueous electrolyte secondary battery of the present inventioncan be fabricated according to a conventional method except for usingthe above-described negative electrode. Examples of the positiveelectrode material which may be used include a transition metal oxidematerial such as lithium transition metal composite oxide (for example,a lithium cobalt composite oxide having a basic composition representedby LiCoO₂, a lithium nickel composite oxide represented by LiNiO₂, and alithium manganese composite oxide represented by LiMnO₂ or LiMn₂O₄) andmanganese dioxide, and a composite oxide mixture thereof. Furthermore,TiS₂, FeS₂, Nb₃S₄, Mo₃S₄, CoS₂, V₂O₅, CrO₃, V₃O₃, FeO₂, GeO₂,LiNi_(0.33)Mn_(0.33)Co_(0.33)O₂, and the like may be used.

The positive electrode material blended with a binder resin is made intoa slurry with an appropriate solvent, and the slurry is coated and driedon a current collector, whereby the positive electrode can be produced.Incidentally, a conductive material such as acetylene black and Ketjenblack is preferably incorporated into the slurry. If desired, athickening agent may be also incorporated.

As the thickening agent and the binder resin, those well known in thisapplication, for example, those described as examples for use in theproduction of the negative electrode, may be used. The blending ratioper 100 parts by weight of the negative electrode material is preferablyfrom 0.5 to 20 parts by weight, more preferably from 1 to 15 parts byweight, for the conductive material, and preferably from 0.2 to 10 partsby weight, more preferably from 0.5 to 7 parts by weight, for thethickening agent.

In the case of making a slurry of the binder resin with water, theblending ratio of the binder resin per 100 parts by weight of thepositive electrode material is preferably from 0.2 to 10 parts byweight, more preferably from 0.5 to 7 parts by weight, and in the caseof making a slurry of the binder resin with an organic solvent capableof dissolving the binder resin, such as N-methylpyrrolidone, theblending ratio is preferably from 0.5 to 20 parts by weight, morepreferably from 1 to 15 parts by weight.

Examples of the positive electrode current collector include aluminum,titanium zirconium, hafnium, niobium, tantalum, and an alloy thereof.Among these, aluminum, titanium, tantalum, and an alloy thereof arepreferred, and aluminum and an alloy thereof are most preferred.

As the electrolytic solution, a conventionally known electrolyticsolution obtained by dissolving various lithium salts in a nonaqueoussolvent can be used. Examples of the nonaqueous solvent which may beused include a cyclic carbonate such as ethylene carbonate, propylenecarbonate, butylene carbonate and vinylene carbonate, a chain carbonatesuch as dimethyl carbonate and ethyl methyl carbonate, a cyclic estersuch as γ-butyrolactone, a cyclic ether such as crown ether,2-methyltetrahydrofuran, tetrahydrofuran, 1,2-dimethyltetrahydrofuranand 1,3-dioxolane, and a chain ether such as 1,2-dimethoxyethane,Usually, some of these are used in combination. Above all, a cycliccarbonate and a chain carbonate, or these solvents and further anothersolvent, are preferably used in combination.

Also, for example, a compound such as vinylene carbonate, vinylethylenecarbonate, succinic anhydride, maleic anhydride, propanesultone anddiethylsulfone, and a difluorophosphate such as lithiumdifluorophosphate, may be added. Furthermore, an overcharge inhibitorsuch as diphenylether and cyclohexylbenzene may be also added.

As the electrolyte that is dissolved in the nonaqueous solvent, forexample, LiClO₄, LiPF₆, LiBF₄, LiCF₃SO₃, LiN(CF₃SO₂)₂, LiN(CF₃CF₂SO₂)₂,LiN(CF₃SO₂)(C₄F₉SO₂) and LiC(CF₃SO₂)₃ may be used. The electrolyte inthe electrolytic solution is preferably used at a concentration ofusually from 0.5 to 2 mol/liter, preferably from 0.6 to 1.5 mol/liter.

As the separator provided to intervene between the positive electrodeand the negative electrode, a porous sheet or nonwoven fabric made ofpolyolefin such as polyethylene and polypropylene is preferably used.

In the nonaqueous electrolyte secondary battery of the presentinvention, the volume ratio negative electrode/positive electrode ispreferably designed to be from 1.01 to 1.5, more preferably from 1.2 to1,4.

EXAMPLES

The present invention is described in greater detail below by referringto Examples, but the present invention is not limited to these Examples.

Incidentally, the particle diameter, tap density, specific surface areaby BET method, true density, X-ray diffraction, coverage ofmultilayer-structure carbon powder material, Raman R and the like asreferred to in the description of the present invention were measured asfollows.

Particle Diameter:

About 20 mg of carbon powder was added to about 1 ml of a 2 (volume) %aqueous solution of polyoxyethylene (20) sorbitan monolaurate, and themixture was dispersed in about 200 ml of ion exchanged water. Theresulting dispersion was measured for the volume-based particle sizedistribution by using a laser diffraction particle size distributionanalyzer (LA-920, manufactured by Horiba Ltd.) to determine the averageparticle diameter (median diameter), the particle diameter d10 of 10%cumulative part, and the particle diameter d90 of 90% cumulative part.The measurement conditions were ultrasonic dispersion for 1 minute, anultrasonic intensity of 2, a circulation velocity of 2, and a relativerefractive index of 1.50.

Tap Density:

The tap density was measured using a powder density measuring apparatus,Tap Denser KYT-3000 (manufactured by Seishin Enterprise Co., Ltd.). Thecarbon powder was caused to fall in a 20-cc tap cell through a sievehaving a sieve opening of 300 μm to fill up the cell and thereafter,tapping with a stroke length of 10 mm was performed 1,000 times. Thedensity here was taken as the tap density.

Average Degree of Circularity:

The measurement of the particle diameter distribution by theequivalent-circle diameter and the calculation of the degree ofcircularity were performed using a flow-type particle image analyzer(FPIA-2000, manufactured by To a Medical Electronics Co. Ltd.). Ionexchanged water was used as the dispersion medium, and polyoxyethylene(20) monomethyl laurate was used as the surfactant. Theequivalent-circle diameter is a diameter of a circle (equivalent circle)having the same projected area of a particle image photographed, and thedegree of circularity is a ratio using the circumferential length of theequivalent circle as the numerator and using the circumferential lengthof a projected particle image photographed as the denominator. Thedegrees of circularity of particles in the measured range of 10 to 40 μmwere averaged, and the obtained value was taken as the average degree ofcircularity.

Specific Surface Area by BET Method:

The measurement was performed using AMS-8000 manufactured by OhkuraRiken Co., Ltd. The sample was pre-dried at 250° C. and after furtherflowing a nitrogen gas for 30 minutes, measured by the BET one-pointmethod based on nitrogen gas adsorption.

Pore Volume (pore volume in the range of 10 to 100,000 nm):

The measurement was performed by a mercury intrusion method using amercury porosimeter (Autopore 9220, model name, manufactured byMicromeritics Corp.). The sample was sealed in a 5-cc powder cell andpretreated (deaeration) by a mercury porosimeter in vacuum (50.Hg) atroom temperature (24° C.) for 10 minutes. Subsequently, the mercurypressure was raised to 40,000 psia from 4.0 psia and then lowered to 15psia (total number of measurement points: 120). At 120 measurementpoints, the amount of mercury intruded was measured after an equilibriumtime of 5 seconds up to 30 psia and after an equilibrium time of 10seconds at each subsequent pressure.

The pore distribution was calculated from the thus-obtained mercuryintrusion curve by using the Washburn equation (D=−(1/P)4γ cos ψ). Here,D represents the pore diameter, P represents the pressure applied, γrepresents the surface tension of mercury (485 dynes/cm was used), and ψrepresents the contact angle (140° was used).

True Density:

The true density was measured by using a pyconometer and using, as themedium, a 0.1 wt % aqueous solution of surfactant (polyoxyethylene (20)monolaurate).

X-Ray Diffraction:

A material prepared by adding and mixing X-ray standard high-puritysilicon powder in a total amount of about 15 wt % with the carbon powderwas measured for a wide-angle X-ray diffraction curve by a reflectiondiffractometer method using, as the radiation source, CuKα raymonochromatized with a graphite monochrometer. The interplanar spacing(d002) and the crystallite size (Lc) were determined using the Gakushinmethod, and 3R/2H was determined from the ratio between the intensity3R(101) of 101 plane based on orientation of the rhombohedral graphitelayer and the intensity 2H(101) of 101 plane based on the hexagonalgraphite layer.

The interplanar spacing (d002) of 002 planes and Lc by the wide-angleX-ray diffraction method of the amorphous carbon for covering thesurface of the spheroidized graphitic particle in the carbon material Awere determined on a sample obtained by firing raw material tar pitchalone (not mixed with graphite particle) at a predetermined temperatureand pulverizing the fired material.

Coverage of Complex-Structure Carbon Material:

The coverage was determined according to the following formula.

Coverage (wt %)=100−(K×D)/((K+T)×N)×100

wherein K represents the weight (Kg) of spherical graphitic carbon usedfor mixing with tar pitch, T represents the weight (kg) of tar pitch asa covering raw material used for mixing with spherical graphitic carbon,D represents the amount of a mixture actually used for firing out of themixture of K and T, and N represents the weight of the coated sphericalgraphitic carbon material after firing.

Raman Measurement:

Using NR-1800 manufactured by JASCO Corp., the intensity IA of the peakPA near 1,580 cm⁻¹ and the intensity 1B of the peak PB in the range of1,360 cm⁻¹ were measured in a Raman spectrum analysis where argon ionlaser light at a wavelength of 514.5 nm was used, and the intensityratio R=IB/IA was determined. The sample was prepared by causing amaterial in a powder state to freely fall in and fill the cell, and themeasurement was performed by irradiating the sample surface in the cellwith laser light while rotating the cell within a plane perpendicular tothe laser light,

Press Load:

An electrode coated in a width of 5 cm was adjusted to the objectivedensity by pressing with a load cell-attached roll of 250 m in diameter.The load required here was measured by the load cell, and the valueobtained was taken as the press load.

Example 1 Production of Carbon Material A

A flake-like graphite particle which is naturally-produced graphite andin which the interplanar spacing (d002) of 002 planes by the wide-angleX-ray diffraction method is 3.36 Å, Lc is 1,000 Å or more, the tapdensity is 0.46 g/cm³, the Raman R value that is a ratio of the peakintensity near 1,360 cm⁻¹ to the peak intensity near 1,580 cm⁻¹ in theargon ion laser Raman spectrum is 0.13, the average particle diameter is28.7 μm, and the true density is 2.27 g/cm³, was used as the rawmaterial graphite.

The flake-like graphite particle was continuously treated using ahybridization system manufactured by Nara Machinery Co., Ltd. under theconditions of a rotor peripheral velocity of 60 in/sec, 10 minutes and atreatment rate of 20 kg/hour, whereby a spheroidization treatment wasperformed while giving a damage to the graphite particle surface.Thereafter, fine powder particles were removed by a classificationtreatment.

In this spheroidized graphitic carbon, the interplanar spacing (d002) of002 planes by the wide-angle X-ray diffraction method was 3.36 Å, Lc was1,000 Å or more, the tap density was 0.83 g/cm³, the Raman R value thatis a ratio of the peak intensity near 1,360 cm⁻¹ to the peak intensitynear 1,580 cm⁻¹ in the argon ion laser Raman spectrum was 0.24, theaverage particle diameter was 11.6 μm, the specific surface ratio by BETmethod was 7.7 m²/g, the true density was 2.27 g/cm³, and the averagedegree of circularity was 0.909.

Subsequently, 100 parts by weight of the spheroidized graphitic carbonobtained above and 9.4 parts by weight of coal tar pitch were mixedunder heating at 160° C. in a mixing machine, and the mixture was firedup to 1,000° C. over 2 weeks in a non-oxidizing atmosphere, then cooledto room temperature, and subjected to pulverization and classification,whereby a multilayer-structure spheroidized carbon material wasobtained.

In this multilayer-structure spheroidized carbon material, theinterplanar spacing (d002) of 002 planes by the wide-angle X-raydiffraction method was 3.36 Å, Lc was 1,000 Å or more, the tap densitywas 0.98 g/cm³, the Raman R value that is a ratio of the peak intensitynear 1,360 cm⁻¹ to the peak intensity near 1,580 cm⁻¹ in the argon ionlaser Raman spectrum was 0.31, the average particle diameter was 11.6μm, the particle diameter d10 was 7.6 μm, the particle diameter d90 was17.5 μm, the specific surface ratio by BET method was 3.5 m²/g, thecoverage was 5.0%, the ratio 3R/2H between the rhombohedral 3R and thehexagonal 2H by the wide-angle X-ray diffraction method was 0.26, andthe pore volume in the range of 10 to 100,000 nm was 0.74 ml/g.

Separately, only the coal tar pitch used above was fired up to 1,300° C.in a nitrogen atmosphere, then cooled to room temperature andpulverized. In the obtained amorphous carbon alone, the interplanarspacing (d002) of 002 planes by the wide-angle X-ray diffraction methodwas 3.45 Å, and Lc was 24 Å,

Production of Carbon Material B

A flake-like graphite particle which is naturally-produced graphite andin which the interplanar spacing (d002) of 002 planes by the wide-angleX-ray diffraction method is 3.36 Å, Lc is 1,000 Å or more, the tapdensity is 0.46 g/cc, the Raman R value that is a ratio of the peakintensity near 1,360 cm⁻¹ to the peak intensity near 1,580 cm⁻¹ in theargon ion laser Raman spectrum is 0.13, the average particle diameter is28.7 μm, and the true density is 2.27 g/cm³, was used as the rawmaterial graphite.

The flake-like graphite particle was continuously treated using ahybridization system manufactured by Nara Machinery Co., Ltd. under theconditions of a rotor peripheral velocity of 60 m/sec, 8 minutes and atreatment rate of 20 kg/hour, whereby a spheroidization treatment wasperformed while giving a damage to the graphite particle surface.

In this spheroidized graphitic carbon, the interplanar spacing (d002) of002 planes by the wide-angle X-ray diffraction method was 3.36 Å, Lc was1,000 Å or more, the tap density was 0.96 g/cm³, the Raman R value thatis a ratio of the peak intensity near 1,360 cm⁻¹ to the peak intensitynear 1,580 cm⁻¹ in the argon ion laser Raman spectrum was 0.22, theaverage particle diameter was 13.4 μm, the particle diameter d10 was 9.3μm, the particle diameter d90 was 19.7 μm, the specific surface ratio byBET method was 7.8 m²/g, the true density was 2.27 g/cm³, the averagedegree of circularity was 0.908, the ratio 3R/2H between therhombohedral 3R and the hexagonal 2H by the wide-angle X-ray diffractionmethod was 0.20, and the pore volume in the range of 10 to 100,000 nmwas 0.68 ml/g.

(Production of Mixed Carbon Material)

The carbon material A and the carbon material B obtained above weremixed such that the ratio of the carbon material B became 30 wt % basedon the total amount of the carbon material A and the carbon material B,whereby a mixed carbon material was obtained. The tap density of themixed carbon material was 0.98 g/cm². The ratio of the average particlediameter of the carbon material A to the average particle diameter ofthe carbon material B was 11.6 m/13.2 μm=0.88.

(Production of Battery for Performance Evaluation)

100 Parts by weight of the mixed carbon material above was added with100 parts by weight of a 1 wt % aqueous solution of carboxymethylcellulose and 2 parts by weight of a 50 wt % water dispersion of styrenebutadiene rubber and kneaded to make a slurry. This slurry was coated ata basis weight of 4.4 mg/cm² on a copper foil by a doctor blade method,then dried at 110° C. and consolidated by a roll press to give a densityof 1.40 g/cc. The press load required for this consolidation was 270 kg.The resulting electrode was cut out to a 32 mm×42 mm rectangle and driedunder reduced pressure at 190° C. to obtain a negative electrode.

85 Parts by weight of lithium-nickel-manganese-cobalt-based compositeoxide powder was added with 10 parts by weight of carbon black, 41.7parts by weight of a 12 wt % N-methylpyrrolidone solution ofpolyvinylidene fluoride, and an appropriate amount ofN-methylpyrrolidone and kneaded to make a slurry, and this slurry wascoated at a basis weight of 8.8 mg/cm² on an aluminum foil by a doctorblade method, dried at 110° C., consolidated by a roll press to give apositive electrode layer density of 2.45 g/cm³, then cut out to a 30mm×40 mm rectangle, and dried at 140° C. to obtain a positive electrode.

The negative electrode and positive electrode obtained above weresuperposed through a separator impregnated with an electrolytic solutionto produce a battery for a charge-discharge test. As the electrolyticsolution, a solution prepared by dissolving LiPF₆ in a mixed solution ofethylene carbonate:dimethyl carbonate:ethyl methyl carbonate=3:3:4 (byweight) to have a concentration of 1 mol/liter was used.

This battery was subjected to initial adjustment by repeating twice anoperation of charging to 4.1 V at 0.2 C, further charging until 0.1 mAwith 4.1 V, then discharging to 3.0 V at 0.2 C, subsequently charging to4.2 V at 0.2 C, further charging until 0.1 mA with 4.2 V, and thereafterdischarging to 3.0 V at 0.2 C.

(Evaluation of Rapid Discharging Property)

After charging to 4.2 V at 0.2 C (charging in 5 hours) and furthercharging for 2 hours with 4.2 V (0.2 C-CCCV), a discharge test to 3.0 Vat 0.2 C (discharging in 5 hours), 1 C (discharging in 1 hour), 2 C(discharging in 0.5 hours), 5 C (discharging in 0.2 hours), 10 C(discharging in 0.1 hours) or 15 C (discharging in 0.07 hours) wasperformed, and the discharge capacity at each rate based on thedischarge capacity at 0.2 C (discharging in 5 hours) was expressed in %.The results are shown in Table 1.

(Evaluation of Rapid Charging Property)

A charge test of charging to 4.2 V at 0.2 C (charging in 5 hours),further charging for 2 hours with 4.2 V (0.2 C-CCCV), and charging to4.2 V at 0.2 C (charging in 5 hours), 1 C (charging in 1 hour), 2 C(charging in 0.5 hours), 5 C (charging in 0.2 hours), 8 C (charging in0.13 hours) or 10 C (charging in 0.1 hours) was performed, and thecharge capacity in each charge test based on the charge capacity whencharged to 4.2 V at 0.2 C (charging in 5 hours) and further charged for2 hours with 4.2 V (0.2 C-CCCV) was expressed in %. The results areshown in Table 1. Incidentally, discharging to 3.0 V at 0.2 C wasperformed after each charging.

(Evaluation of Cycle Characteristics)

Charging to 4.2 V at 2 C and discharging to 3.0 V at 3 C of the batteryabove were repeated, and the discharge capacities at 300th cycle and500th cycle based on the discharge capacity at 1st cycle were expressedin % as a 300-cycles sustaining ratio and a 500-cycles sustaining ratio,respectively. The results are shown in Table 1.

Example 2

This was performed in the same manner as in Example 1 except forchanging the ratio of the carbon material B to 50 wt % based on thetotal amount of the carbon material A and the carbon material B. Theresults are shown in Table 1.

Comparative Example 1

This was performed in the same manner as in Example 1 except for notmixing the carbon material B with the carbon material A. The results areshown in Table 1.

Comparative Example 2 Production of Carbon Material A

A flake-like graphite particle which is naturally-produced graphite andin which the interplanar spacing (d002) of 002 planes by the wide-angleX-ray diffraction method is 3.36 Å, Lc is 1,000 Å or more, the tapdensity is 0.46 g/cm³, the Raman R value that is a ratio of the peakintensity near 1,360 cm⁻¹ to the peak intensity near 1,580 cm⁻¹ in theargon ion laser Raman spectrum is 0.13, the average particle diameter is28.7 μm, and the true density is 2.27 g/cm³, was used as the rawmaterial graphite.

The flake-like graphite particle was continuously treated using ahybridization system manufactured by Nara Machinery Co., Ltd. under theconditions of a rotor peripheral velocity of 60 m/sec, 10 minutes and atreatment rate of 20 kg/hour, whereby a spheroidization treatment wasperformed while giving a damage to the graphite particle surface.Thereafter, fine powder particles were removed by a classificationtreatment.

In this spheroidized graphitic carbon, the interplanar spacing (d002) of002 planes by the wide-angle X-ray diffraction method was 3.36 Å, Lc was1,000 Å or more, the tap density was 0.83 g/cm³, the Raman R value thatis a ratio of the peak intensity near 1,360 cm⁻¹ to the peak intensitynear 1,580 cm⁻¹ in the argon ion laser Raman spectrum was 0.24, theaverage particle diameter was 11.6 μm, the specific surface ratio by BETmethod was 7.7 m²/g, the true density was 2.27 g/cm³, and the averagedegree of circularity was 0.909.

Subsequently, 100 parts by weight of the spheroidized graphitic carbonobtained above and 10 parts by weight of petroleum-derived pitch werecharged into Loedige mixer manufactured by MATSUBO Corporation, kneadedat 90° C., thereafter fired up to 1,300° C. over 2 hours in a nitrogenatmosphere, held for 2 hours, then cooled to room temperature, andfurther subjected to pulverization and classification, whereby amultilayer-structure spheroidized carbon material was obtained.

In this multilayer-structure spheroidized carbon material, theinterplanar spacing (d002) of 002 planes by the wide-angle X-raydiffraction method was 3.36 Å, Lc was 1,000 Å or more, the tap densitywas 0.99 g/cm³, the Raman R value that is a ratio of the peak intensitynear 1,360 cm⁻¹ to the peak intensity near 1,580 cm⁻¹ in the argon ionlaser Raman spectrum was 0.22, the average particle diameter was 11.6μm, the particle diameter d10 was 7.7 the particle diameter d90 was 17.5μm, the specific surface ratio by BET method was 3.8 m²/g, the truedensity was 2.27 g/cm³, the coverage was 3.0%, the ratio 3R/2H betweenthe rhombohedral 3R and the hexagonal 2H by the wide-angle X-raydiffraction method was 0.24, and the pore volume in the range of 10 to100,000 nm was 0.62 ml/g.

Separately, only the coal-derived pitch used above was fired up to1,300° C. in a nitrogen atmosphere, then cooled to room temperature andpulverized. In the obtained amorphous carbon alone, the interplanarspacing (d002) of 002 planes by the wide-angle X-ray diffraction methodwas 3.45 Å, and Lc was 22 Å.

Others were performed in the same manner as in Comparative Example 1.The results are shown in Table 1.

Comparative Example 3 Carbon Material A

The same carbon material as the carbon material A in Comparative Example2 was used.

Carbon Material B

A commercially available graphitic particle, SFG44, produced by TIMCALwas used. In this SFG44, the interplanar spacing (d002) of 002 planes bythe wide-angle X-ray diffraction method was 3.36 Å, Lc was 1,000 Å ormore, the tap density was 0.44 g/cm³, the Raman R value that is a ratioof the peak intensity near 1,360 cm⁻¹ to the peak intensity near 1,580cm⁻¹ in the argon ion laser Raman spectrum was 0.10, the averageparticle diameter was 25.4 μn, the particle diameter d10 was 7.5 μm, theparticle diameter d90 was 46.5 μm, the specific surface ratio by BETmethod was 4.4 m²/g, the true density was 2.27 g/cm³, the average degreeof circularity was 0.84, the ratio 3R/2H between the rhombohedral 3R andthe hexagonal 2H by the wide-angle X-ray diffraction method was 0.28,and the pore volume in the range of 10 to 100,000 nm was 1.30 ml/g.

(Production of Mixed Carbon Material)

The carbon material A and the carbon material B obtained above weremixed such that the ratio of the carbon material B became 30 wt % basedon the total amount of these carbon materials, whereby a mixed carbonmaterial was obtained. The tap density of the mixed carbon material was0.82 g/cm³. The ratio of the average particle diameter of the carbonmaterial A to the average particle diameter of the carbon material B was11.6 m/25.4 μm=0.46. Others were performed in the same manner as inExample 1. The results are shown in Table 1.

Comparative Comparative Comparative Items Unit Example 1 Example 2Example 1 Example 2 Example 3 Properties of Carbon Material A d002 Å3.36 3.36 3.36 3.36 3.36 Lc Å >1000 >1000 >1000 >1000 >1000 Raman R 0.310.31 0.31 0.22 0.22 Tap density g/cm³ 0.98 0.98 0.98 0.99 0.99 3R/2H0.26 0.26 0.26 0.24 0.24 Average particle diameter μm 11.6 11.6 11.611.6 11.6 Particle diameter d10 μm 7.6 7.6 7.6 7.7 7.7 Particle diameterd90 μm 17.5 17.5 17.5 17.5 17.5 BET Specific surface area m²/g 3.5 3.53.5 3.8 3.8 Pore volume ml/g 0.74 0.74 0.74 0.62 0.62 Coverage % 5.0 5.05.0 3.0 3.0 Average degree of circularity of 0.909 0.909 0.909 0.9090.909 0.909 spheroidized graphitic particle before covering d002 ofcovering amorphous carbon alone Å 3.45 3.45 3.45 3.45 3.45 Lc ofcovering amorphous carbon alone Å 24 24 24 22 22 Properties of CarbonMaterial B d002 Å 3.36 3.36 — — 3.36 Lc Å >1000 >1000 — — >1000 Raman R0.22 0.22 — — 0.10 Tap density g/cm³ 0.96 0.96 — — 0.44 3R/2H 0.20 0.20— — 0.28 Averaqe particle diameter μm 13.4 13.4 — — 25.4 Particlediameter d10 μm 9.3 9.3 — — 7.5 Particle diameter d90 μm 19.7 19.7 — —19.7 BET Specific surface area m²/g 7.8 7.8 — — 4.4 Pore volume ml/g0.68 0.68 — — 1.30 True density g/cm³ 2.27 2.27 — — 2.27 Averaqe deqreeof circularity 0.908 0.908 — — 0.840 Mixed Carbon Material Ratio ofcarbon material B based on total wt % 30 50 0 0 30 amount of carbonmaterial A and carbon material B Average particle diameter ratio between0.88 0.88 — — 0.46 carbon material A and carbon material B Tap densityg/cm³ 0.98 0.99 — — 0.82 Press load kg 270 210 320 400 26 RapidDischarge Characteristics 0.2 C Discharge capacity mAh 13.6 13.1 13.413.5 13.4 1 C Discharge/0.2C discharge % 95 94 96 95 94 2 CDischarge/0.2C discharge % 92 90 92 92 90 5 C Discharge/0.2C discharge %86 84 86 86 80 10 C Discharge/0.2C discharge % 70 74 71 68 65 15 CDischarge/0.2C discharge % 32 41 35 22 20 Rapid Charge Characteristics0.2 C-CCCV Charge capacity mAh 13.3 13.7 13.6 13.3 13.4 0.2 CCharge/0.2C-CCCV Charge % 98 98 98 97 97 1 C Charge/0.2C-CCCV Charge %96 96 96 93 93 2 C Charge/0.2C-CCCV Charge % 94 94 94 90 88 5 CCharge/0.2C-CCCV Charge % 87 86 86 81 78 8 C Charge/0.2C-CCCV Charge %73 70 74 64 60 10 C Charge/0.2C-CCCV Charge % 52 57 55 40 35 Cyclecharacteristics 300-Cycles sustaining ratio % 59 90 36 20 25 500-Cyclessustaining ratio % 42 88 30 15 20

As seen in Table 1, in Examples 1 and 2 using the negative electrodematerial according to the present invention, excellent rapidcharging-discharging properties and cycle characteristics wereexhibited. On the other hand, in Comparative Example using a negativeelectrode material out of the scope of the present invention, the cyclecharacteristics were poor, and in Comparative Examples 2 and 3, therapid charging-discharging properties and the cycle characteristics werelow.

INDUSTRIAL APPLICABILITY

The nonaqueous electrolyte secondary battery comprising an electrodeusing the negative electrode material of the present invention exhibitsexcellent properties satisfying both rapid charge-dischargecharacteristics and high cycle characteristics.

While the invention has been described in detail and with reference tospecific embodiments thereof, it will be apparent to one skilled in theart that various changes and modifications can be made therein withoutdeparting from the spirit and scope of the invention.

This application is based on Japanese Patent Application (PatentApplication No. 2009-079945) filed on Mar. 27, 2009, the entirety ofwhich is incorporated herein by way of reference.

1. A negative electrode material for nonaqueous electrolyte secondarybattery, comprising the following carbon material A and carbon materialB: (Carbon material A) a multilayer-structure carbon material containinga graphitic particle and an amorphous carbon covering the surface of thegraphitic particle, which is a carbon material where the interplanarspacing (d002) of 002 planes by the wide-angle X-ray diffraction methodis 3.37 Å or less, Lc is 900 Å or more, the tap density is 0.8 g/cm³ ormore, and the Raman R value that is a ratio of the peak intensity near1,360 cm⁻¹ to the peak intensity near 1,580 cm⁻¹ in the argon ion laserRaman spectrum, is from 0.25 to 0.6, (Carbon Material B) a graphiticparticle where the interplanar spacing (d002) of 002 planes by thewide-angle X-ray diffraction method is 3.37 Å or less, Lc is 900 Å ormore, the tap density is 0.8 g/cm³ or more, the Raman R value that is aratio of the peak intensity near 1,360 cm⁻¹ to the peak intensity near1,580 cm⁻¹ in the argon ion laser Raman spectrum, is from 0.2 to 0.5,and the average degree of circularity as determined by a flow-typeparticle analyzer is 0.9 or more.
 2. The negative electrode material fornonaqueous electrolyte secondary battery as claimed in claim 1, whereinthe ratio in the average particle diameter between the carbon material Aand the carbon material B (average particle diameter of carbon materialA/average particle diameter of carbon material B) is from 0.7 to 1.3. 3.The negative electrode material for nonaqueous electrolyte secondarybattery as claimed in claim 1, wherein the ratio of the carbon materialB is from 30 to 70 wt % based on the total amount of the carbon materialA and the carbon material B.
 4. The negative electrode material fornonaqueous electrolyte secondary battery as claimed in claim 1, whereinin the graphitic particle used for the carbon material A, theinterplanar spacing (d002) of 002 planes by the wide-angle X-raydiffraction method is 3.37 Å or less, Lc is 900 Å or more, the tapdensity is 0.8 g/cm³ or more, and the Raman R value that is a ratio ofthe peak intensity near 1,360 cm⁻¹ to the peak intensity near 1,580 cm⁻¹in the argon ion laser Raman spectrum is from 0.2 to 0.5.
 5. Thenegative electrode material for nonaqueous electrolyte secondary batteryas claimed in claim 1, wherein the tap density is 0.8 g/cm³ or more. 6.The negative electrode material for nonaqueous electrolyte secondarybattery as claimed in claim 1, wherein the true density of the carbonmaterial B is 2.21 g/cm³ or more.
 7. The negative electrode material fornonaqueous electrolyte secondary battery as claimed in claim 1, whereinthe specific surface area of the carbon material A is from 0.5 to 8m²/g.
 8. The negative electrode material for nonaqueous electrolytesecondary battery as claimed in claim 1, wherein the average degree ofcircularity of the graphitic particle used for the carbon material A asdetermined by a flow-type particle analyzer, is 0.88 or more.
 9. Thenegative electrode material for nonaqueous electrolyte secondary batteryas claimed in claim 1, wherein the pore volumes in the range of 10 to100,000 nm of the carbon material A and the carbon material B asmeasured by the mercury intrusion method, are 0.4 ml/g or more.
 10. Thenegative electrode material for nonaqueous electrolyte secondary batteryas claimed in claim 1, wherein the average particle diameter of thecarbon material A is from 2 to 30 μm.
 11. A negative electrode fornonaqueous electrolyte secondary battery, comprising: a currentcollector; and a negative electrode layer provided thereon, wherein thenegative electrode layer contains the negative electrode material fornonaqueous electrolyte secondary battery claimed in claim 1 and a binderresin.
 12. A nonaqueous electrolyte secondary battery comprising thenegative electrode claimed in claim 11, a positive electrode capable ofstoring/releasing lithium ion, and a nonaqueous electrolytic solution.